ECHINOCOCCUS ALTRICJPAEIENS. 221 



to the development, at least in this case it will never attain to 

 the size of the mother-vesicles of Echinococcus which we meet 

 with in other places. The fluid will therefore be reduced to a 

 minimum, and the development of the young will be more 

 sparing. Moreover, Echinococci usually only proliferate on cer- 

 tain places; others remain quite barren. It appears to me that 

 the former takes place usually more towards the bottom of the 

 tumour than at its upper part. Then in each particular case 

 the same mode of development certainly occurs, which is proper 

 to the species of Echinococcus. In the domestic animals we 

 usually find in the gelatinous masses the simple formation of 

 scolices (Echinoc. scolicipariens}. In the cases of Zeller and 

 Virchow we see the complicated scolex-formation, namely, the 

 simultaneous production of scolices and nurses (Echinoc. altrici- 

 pariens). But within these lymphatic vessels a peculiar process 

 of constriction appears to go on sooner or later. Individual 

 runners may be separated by constriction from the main vesicle 

 by the contraction of the lymphatics in particular places, and 

 then continue to grow on their own account. They are fre- 

 quently still attached to the parent-vesicle by a scarcely per- 

 ceptible thread (vide Zeller) ; perhaps even this thread is cut 

 off by constriction, and we have isolated, or apparently isolated, 

 separate vesicles, which perhaps may still betray a connection 

 with the main vesicle on close examination. But if this constric- 

 tion has taken place, and the separated vesicle continues its 

 proper life, it will probably retain the degree of proliferation 

 belonging to it during its life in connection with the main vesicle. 

 If the space of the mother-cyst cut off were proliferant, it will 

 continue to proliferate, and if not it will probably not do so. 

 Thus we may explain why the vesicles placed towards the peri- 

 phery are without scolices, daughter-vesicles, and hooks, as the 

 upper part of the main cyst, from which they are separated by 

 constriction, is rarely proliferant. In this way also we may 

 easily explain the occurrence of sterile cysts in other parts of 

 such livers. A single six-hooked embryo, therefore, may be 

 the cause of many isolated Echinococci of the liver, or acephalo- 

 cysts. This gives us the best key for the explanation of Virchow's 

 second, third, fourth, and fifth points. I agree with Yirchow, 

 therefore, also when he speaks of a multiplication of Echinococci 

 from a single vesicle in such cases, but only if he understands a 

 constriction of this kind in that case. In no other way can we 



